Variations in Parathyroid Hormone Concentration in Patients with Low 25 Hydroxyvitamin D

Unlabelled: Although 25 hydroxyvitamin D (25OHD) and parathyroid hormone (PTH) levels are inversely related, less than half of the patients with a low vitamin D level have an elevated PTH, and, in most of these patients, the PTH does not immediately normalize with correction of the vitamin D.

Introduction: Despite the inverse relationship between 25OHD and PTH, patients with vitamin D deficiency seen in clinical practice do not always have an elevated PTH, and, in those with secondary hyperparathyroidism, the PTH does not always normalize with correction of vitamin D deficiency. We examined variations in PTH concentrations in patients with low 25OHD and studied changes in the PTH concentration with restoration of vitamin D sufficiency.

Methods: This was a retrospective cohort study of patients with a 25OHD < 30 ng/mL and a concomitant PTH measurement seen at the Metabolic Bone Disease Clinic at a tertiary care center between July 1, 2007 and May 31, 2011. Patients with conditions associated with alterations in PTH were excluded.

Results: The study population consisted of 104 patients. The mean age was 55.5 years, and 83 % were female. The 25OHD and PTH were negatively correlated, but only 30 % of patients with a 25OHD < 30 ng/mL and 40 % of those with a 25OHD < 20 ng/mL had an elevated PTH. As the 25OHD increased to 30 ng/mL or higher, the PTH decreased significantly in the group of patients who had an elevated PTH at baseline, but only 44 % reached a normal PTH. Of patients with a normal PTH at baseline, 59 % experienced a drop in their PTH while the PTH remained unchanged or increased in 41 %.

Conclusions: PTH has a limited role in defining vitamin D status in individual patients and in guiding vitamin D therapy in clinical practice.